When treating cancer tumors the doctor is preparing the treatment e.g. by planning how large the dose of the medicine shall be or how much the radiation therapy shall comprise. Basis for the planning of the radiation therapy is done e.g. by using computer tomography images. These images are nowadays more and more frequently combined with images from other media such as magnetic camera images (a magnetic camera is normally referred to as MRI=magnetic resonance imaging) and images from a PET camera (PET=Positron Emission Tomography) in order with more certainty to determine the tumor/-s extension in all directions.
In order to minimize the side effects on normal healthy tissue repeatedly radiation doses normally are given. At these times of treatment it is important to carefully reposition the body and the tumor area according to predetermined parameters so the tumor area not will be missed.
Electronic image giving plates have been used for many years in order to control the position of the skeleton when using high energetic therapy beams on 4-20 megavolts (MV), which normally are used. In recent years the beam accelerators that give rise to the radiation doses have been equipped with complementary equipment resulting in x-ray beams in the kilovolt area (kV). These beams in the kV area have properties differentiated from the high energetic MV beam. The beams in the kV area are decelerated not only by the mass coming in its way, but also by a decelerating force in relation to the density of the material that the beams are passing by and the decelerating force is increasing almost exponentially with higher density.
Positioning markers are used in order to show the location of a tumor in a human or an animal tissue. These markers are decelerating the x-ray beams so much that the marker becomes visible on monitors where the results from different media are shown. Gold has a high density of 19.3 g/cm3, which makes it advantageously to be used as decelerating substance for the beams. Pure gold is also soft and possible to shape and is tolerated by the body since it is an inert material. The volume of gold may be limited so the substance becomes a thin wire, which also means that the marker may be inserted into the body be means of thin needles. Thereby the risk of bleedings and infections is minimized. Such a marker of gold is known by e.g. WO2006/004542 A1.
X-ray beams passing a body with a diameter of up until 60 cm give an image on the monitor by means of the beams having been decelerated to a varying extent in different parts of the tissue. If a small positioning marker of ca 0.25-1.2 mm in the tissue shall be able to influence the image the x-ray beams hitting on the marker must decelerate the x-ray beams to such extent that contrasting differences are giving in the image.
Markers that are put into tissue of human or animal will rest mainly in the same place the entire life. Thus, it is extremely important that the markers not cause mechanical damage or give rise to allergies or other state of ill-health. The marker must have sufficient size and have an appropriate density in order for the marker to be clearly depicted at MR examination.
The inventor has identified a need when using positioning markers of gold, which is related to the difficulty to make them visible on monitors from all media that are used in order to determine the extension of the tumor. In order to facilitate such that the images from the computer tomography and the magnetic camera may be superposed in the appropriate way it would be desirable that the positioning marker also is visible when using a magnetic camera. As an example small positioning markers of gold are not visible on magnetic camera images.
The purpose with the present invention is thus, to achieve a positioning marker that is visible on monitors for the majority of media being used in order to optimize the beam treatment planning. Further the marker shall satisfy the demands to be tolerated of the body and not to cause mechanical damage in the body of the person in which the marker is inserted.